Geochemistry and petrogenesis of rare-metal pegmatites: A case study of Lemera Sn ore deposits in Kivu region of Karagwe-Ankole Belt, D. R. Congo

Abstract

This paper reports the results from an investigation on petrogenesis and geochemistry of the Lemera granite pegmatites in Kivu region of Karagwe-Ankole Belt, D. R. Congo and the related tin ore deposits. Seven granite pegmatite samples were collected from outcrops and analyzed for bulk-rock geochemistry analysis using ICP-MS and XRF spectrometry. The analyzed samples show a relative abundance of Al2O3 over Fe2O3(T) and MgO (12.95, 0.96, and 0.16, all in wt.%, on average and respectively). The alumina saturation index ranges from 1.33 to 2.05. The abundances of some important rare metals, as well as some related key parameters, are as follows: Sn ((1–138)×10-6), Ta ((0.20–0.60)×10−6), Nb ((1–8)×10-6), Cs ((1.20–3.20)×10−6), Rb ((3–223)×10−6), Zr ((7–201)×10−6), w(K)/w(Rb) (150–272); w(K)/w(Cs) (9.06–23.3); w(Nb)/w(Ta) (3.33–14). The results indicate that the Lemera granite pegmatites crystallized from a fertile, peraluminous, and S-type granitic magma through a fractional crystallization process in a late to post-collisional setting. Mineralization of Sn and Zr of Lemera granite pegmatites is noticed.